Sorry for the newbie question (in case it has been asked before) but I just went through the pains of changing the spark plugs on my 97 F150 with a 5.4 Triton, and then found that there was excellent instructions on this forum - I wish I would've found this forum first!
Anyway, my check engine light came on a month or so ago, and with around 70K on the truck, I first figured an O2 sensor. I was at Checker Auto and they had the AutoXray EXLink OBD tester there for $200 - the same kit with all the cables was over $400 (that was the cheapest I could find it on the 'net). I hooked the EXLink up to my truck, it identified code P131, which my book identified as "Upstream heated O2 sensor circuit low voltage, bank 1". I was informed by the local parts store that on this type of truck, "bank 1" meant the odd number cylinders or the drivers side (someone please confirm this). At any rate, the truck has 4 O2 sensors, 2 before the catalytic converter (upstream), and 2 after the converter (downstream). Bank 1, upstream meant drivers side, before the converter obviously. $50 later, I put the new O2 sensor on (the parts store, AutoZone, lent me a VERY nice tool that made the job easy, all I had to do was put a small deposit down, I *highly* recommend checking this out!), hooked up my EZLink, cleared the check engine light and was happy as a clam.
About 100 miles later though, I have another check engine light. I called the Ford dealership to see if they would help and a pretty cool guy did some checking for me. I was getting a new code, this one was P171, from my book it is "System Adaptive fuel too lean, bank 1". The guy at Ford told me it could be anything from a leaky head gasket to the pcv valve. He "suggested" that I simply bring it in to Ford and let them dink around with it. Nah, the reason I bought my own code reader is because I don't want to have someone else dink around with my truck.
Does anyone have any suggestions about this new code? I did clear the code, making the check engine light go away, but it only took about 20 miles and the same code comes back. I know whatever is wrong is probably the same reason that the O2 sensor went out for, it is the same bank, etc. Keep in mind I just put all new filters on (air and oil), recently changed the oil, and has 8 new spark plugs in it. I was, very much, in need of this tune up, which probably doesn't help matters much. The computer may just need some time to readjust, I don't know.
I thought I would ask on this VERY cool forum, hopefully I didn't put anyone to sleep with my long message.
Thanks, in advance, for any help!

 

dwayneh,

Lean codes are often the result of "unmetered" air getting into the combustion chamber. The computer doesn't "know" about this extra air and can not compensate for it with extra fuel.

A dirty MAF sensor can let more air by than it can measure. Clean your MAFs. Although dirty MAFs usually results in lean codes for banks 1&2.

Next look for vacuum leaks. Broken , cracked or detached vacuum lines. There is an elbow shaped boot vacuum connection at the back of the throttle body that often goes bad. Check it out.

You can also check for cracked intake or bad gasket by spraying TB cleaner around your intake manifold. If your engine idle picks up RPM there's your leak. I hope that is not the case.

Good Luck,

Bill

 

Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit

Possible causes:

Fuel system

Excessive fuel pressure.
Leaking fuel injector(s).
High fuel pressure.
Low fuel pressure.
Contaminated fuel injector(s)

Ignition system

Spark plugs.
Spark plug wires.
Coils.

Induction system

Air leaks after the MAF sensor assembly.
Vacuum leaks.
Restricted air inlet.
PCV system.
Improperly seated engine oil dipstick.

Base engine

Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2S(s).
Check intake air system for leaks, obstructions and damage.
Check air cleaner element, air cleaner housing for blockage.
Verify fuel level.
Verify integrity of the PCV system.
Check for disconnected spark plug wires.
Check for vacuum leaks.
Verify customer did not run out of fuel.

 

Wow, this forum is GREAT! Thank you both for the quick responses, I'll do some checking around to see what I can come up with.... silly question, what *is* an MAF? Sorry, I don't remember seeing that one...

 

Mass Airflow Sensor. Its a round sensor attached to your air intake. It measures air flow and reports it to the computer. It helps the computer determine proper air/fuel ratio.

 

some unknowledgeable people (including some dealers) will tell you that the maf must be replaced and can not be serviced.

You need a tamperproof torx bit to get the bolts off the top of it, about two bucks at napa. A regular torx will not work, the tamperproof torx that ford uses has a dimple in the middle of it.

Anyway, i think the size is T20 tampeproof, don't quote me though.

Unplug the wiring harness from the maf, remove the screws from the top of the sensor, and CAREFULLY pull the sensor out and lay it down on your workbench.

Don't touch the maf wires with anything, or allow them to touch anything.

Just spray some electrical parts cleaner all over the maf wires and the posts to get the black gunk off them and let it evaporate.

Install the sensor back in the housing carefully. Note the arrow pointing out airflow, it only goes in one way. Install the screws and plug in the maf wiring harness into the maf.

Reset the EEC by pulling the EEC fuse and cranking the car (it won't start with no fuse)

Reinstall the fuse, and start the car. You will notice by pulling the eec fuse and cranking, you have cleared the codes to the eec.

If your problem was indeed a dirty maf then you will notice the check engine light will not come back on.

Take it easy for the next 5 miles or so, as the eec needs to relearn several strategies.

Ford has a method to relearn the eec, but it basically involves just taking the car out for a long cruise and keep your foot out of it for about 5-10 miles.

Dirty mafs, another reason to use a paper filter versus an oiled one.

JH

Replace the

 

Cleaning the MAF on a 5.4 is a bit different. It is inside the hose end of the air cleaner housing. You dont need any tools to get at it. Take a look in the FAQs near the top of the forum page for some instructions and a picture.

 

good post, i'm not familar with the 5.4 setup. I am a 4.6 guy of sorts.

JH

 

Justin thats a good tip about paper vs. oiled filters too.
It's a pet peeve of mine
I use a K&N on the race car but that's different.